The present invention relates to voltage regulators and in particular to switching voltage regulators for DC to DC voltage regulation.
Computer systems can emit electromagnetic radiation at various frequencies. Those emissions may cause undesirable electromagnetic interference (xe2x80x9cEMIxe2x80x9d) with the circuitry of the computer system and other electronic equipment near the computer system. For that reason, the FCC has enacted certain Open Chassis EMI regulations that impose limits on the electromagnetic emissions that such systems generate. 47 CFR xc2xa715.109. These limits are specified in Table 1 below.
Currently, system designers are primarily concerned with the radiation produced when certain signals (to be transmitted between various components) are driven at certain periodic frequencies, and with the radiation generated by components that operate at high frequency, e.g., microprocessors. As the development of computer systems has advanced, however, other components are beginning to contribute electromagnetic emissions that make it increasingly difficult to pass these FCC regulations.
One class of components beginning to contribute to this problem comprises voltage regulators. To meet the increasing power delivery requirements of certain components (e.g., microprocessors), voltage regulator circuits must increase their frequency of operationxe2x80x94to ensure they will not require unacceptably large inductors and capacitors to perform their function. Such circuits may be required to operate at several hundred kHz to 1 MHz, or even higher. Such frequencies"" harmonics may produce electromagnetic emissions that make it increasingly difficult to pass the FCC""s Open Chassis EMI regulations for the 30-88 MHz range.
Making matters worse is that multi-phase voltage regulators are beginning to replace single-phase devices. Such multi-phase components operate at a frequency that is a multiple of the frequency at which signals are driven for each phase. For example, a four phase 1 MHz voltage regulator has an EMI signature like that of a device that operates at a 4 MHz fundamental frequency. EMI producing harmonics for such a device may easily reach the 30-88 MHz range. Although the emissions these components generate can be reduced by placing various types of Faraday cages (or other sealing/covering apparatus) over them, such devices add cost to the system, may occupy scarce motherboard space, and may impose challenging signal routing requirements. As a consequence, using such devices to address this issue is not a particularly attractive solution.
Accordingly, there is a need for an improved voltage regulator. There is a need for such a device that can operate at a high frequency without causing unacceptable EMI. There is also a need for such a device that can be integrated into standard system designs without requiring significant modification (e.g., without requiring placement of various types of EMI shielding components over the voltage regulator). The voltage regulator of the present invention provides such a device.